An apparatus which is implanted in a living body to generate an electrical stimulus for therapeutic purpose, such as a nerve stimulator and a muscle stimulator, is composed of an implantable stimulation generator serving as a power source portion and an implantable electrode lead including an electrode and a lead. The present invention relates to an implantable electrode lead, and particularly to an implantable lead which includes a lubricant coating layer on a specified portion thereof and in which operability at the time of implanting is improved and the inflammation and the patient's feeling of physical disorder generated after the implanting are lessened.
Conventionally, there have been used cardiac pacemakers, defibrillators, nerve stimulators, pain alleviators, epilepsy treating apparatus, electric muscle stimulators and the like, which are apparatus for conducting treatment by giving an electrical stimulus directly or indirectly to the heart, nerve, brain, muscle or the like. These apparatus are each composed of an implantable stimulation generator having a power source and generating an electrical stimulus, and an implantable electrode lead for transmitting the generated electrical stimulus to the site on which the stimulus is to act.
Particularly, the nerve stimulator, pain alleviator, epilepsy treating apparatus, and muscle stimulator are apparatus for conducting treatment by giving an electrical stimulus directly to the nerve, brain or muscle, and in each of the apparatus it is necessary to cause the electrode lead to indwell in the living body for the purpose of giving a target site the electrical stimulus generated by the implantable stimulation generator. For this reason, the implantable electrode lead in each of the apparatus is composed of:
At least one electrode for giving an electrical stimulus to the nerve, brain, muscle or the like;
A connector for electrical connection to the implantable stimulation generator of the nerve stimulator, pain alleviator, epilepsy treating apparatus, muscle stimulator or the like; and
A conductor portion composed of an electrical conductor and an insulator covering the outside of the electrical conductor.
Incidentally, an implantable electrode lead to be used in a subcutaneous manner has a structure in which the electrode is connected to the nerve, brain, muscle or the like, most part of the conductor portion is inserted under the subcutaneous tissue, and the conductor portions thus inserted under the subcutaneous tissue is connected to the implantable stimulation generator of the nerve stimulator, pain alleviator, epilepsy treating apparatus, muscle stimulator or the like through a connector. The subcutaneous tissue herein means a tissue located between the skin and a muscle.
Now, one example of the conventional implantable electrode lead will be described below.
The implantable electrode lead is composed of a proximal portion having a connector for connection to the implantable stimulation generator of the nerve stimulator or the like, a distal portion having an electrode set in contact with the target site so as to give an electrical stimulus to the target site, a conductor portion connected to the proximal portion and the distal portion so as to transmit the electrical stimulus, and a fixation portion provided on a part of the outside surface of the conductor portion so as to fix the implantable electrode lead in the living body.
At the time of implanting, the electrode of the implantable electrode lead is connected to the target site of the nerve, brain, muscle or the like, and the fixation portion is fixed to the living body, whereby the electrode is prevented from moving. Further, the connector is laid under the subcutaneous tissue and connected to the implantable stimulation generator. In mounting the implantable electrode lead, the implantable stimulation generator is in many cases disposed remote from the electrode, and the proximal portion is in some cases moved to the implantable stimulation generator by passing it under the subcutaneous tissue over a long distance. In many case, however, the insulator on the implantable electrode lead is formed of a silicone, which is a polymer high in bio-stability and durability, and the silicone has a comparatively high coefficient of dynamic friction in relation to the subcutaneous tissue, so that it is difficult to pass the implantable electrode lead under the subcutaneous tissue.
On the other hand, for the purpose of facilitating the passage of the implantable electrode lead under the subcutaneous tissue, it is in some cases practiced to preliminarily insert a subcutaneous tunneling tool under the subcutaneous tissue and to pass the implantable electrode lead through the inside of a lumen of the subcutaneous tunneling tool. However, since the silicone used for forming the insulator on the conductor portion of the implantable electrode lead generates a high frictional force on the inside wall of the lumen, the performance of passage of the implantable electrode lead in the lumen is low, so that it is difficult to smoothly pass the proximal portion under the subcutaneous tissue, even by use of the subcutaneous tunneling tool.
An electrode lead for a cardiac pacemaker in which the surface of a conductor portion is coated with a hydrophilic polymer for reducing the frictional force on the surface of a silicone-made electrode lead and thereby promising an easier sliding of the electrode lead has been disclosed (see Japanese Patent Laid-open No. Hei 8-10338). In the electrode lead described in Japanese Patent Laid-open No. Hei 8-10338, however, the conductor portion is coated with the hydrophilic polymer up to the tip end of the electrode lead, and the publication does not include a description that the electrode lead includes a fixation portion. Therefore, it is difficult to stably fix the implantable electrode lead in a comparatively broad space, although it may be possible to stably fix the electrode lead in a narrow place such as in a blood vessel. Even in the case where the implantable electrode lead has a fixation portion, the structure in which the conductor portion is entirely coated with the hydrophilic polymer results in that the surface of the conductor portion is slippery and it is impossible to stably fix the implantable electrode lead in a living body.